Human cancers harbor numerous genetic and epigenetic alterations, generating neoantigens potentially recognizable by the immune system (Sjoblom et al. (2006) Science 314:268-74). The adaptive immune system, comprised of T and B lymphocytes, has powerful anti-cancer potential, with a broad capacity and exquisite specificity to respond to diverse tumor antigens. Further, the immune system demonstrates considerable plasticity and a memory component. The successful harnessing of all these attributes of the adaptive immune system would make immunotherapy unique among all cancer treatment modalities.
Until recently, cancer immunotherapy had focused substantial effort on approaches that enhance anti-tumor immune responses by adoptive-transfer of activated effector cells, immunization against relevant antigens, or providing non-specific immune-stimulatory agents such as cytokines. In the past decade, however, intensive efforts to develop specific immune checkpoint pathway inhibitors have begun to provide new immunotherapeutic approaches for treating cancer, including the development of an antibody (Ab), ipilimumab (YERVOY®), that binds to and inhibits CTLA-4 for the treatment of patients with advanced melanoma (Hodi et al., 2010) and the development of antibodies such as nivolumab and pembrolizumab (formerly lambrolizumab; USAN Council Statement, 2013) that bind specifically to the Programmed Death-1 (PD-1) receptor and block the inhibitory PD-1/PD-1 ligand pathway (Topalian et al., N Engl J Med 366:2443-54 (2012a); Topalian et al., Curr Opin Immunol 24:207-12 (2012b); Topalian et al., J Clin Oncol 32(10):1020-30 (2014); Hamid et al., N Engl J Med 369:134-144 (2013); Hamid and Carvajal, Expert Opin Biol Ther 13(6):847-61 (2013); McDermott and Atkins, Cancer Med 2(5):662-73(2013)).
Targeted therapy of multiple non-redundant molecular pathways regulating immune responses may enhance antitumor immunotherapy. However, not all combinations have acceptable therapies. There remains a need for combination therapies with an acceptable safety profile and high efficacy that enhance antitumor immune responses compared to monotherapy and other immunotherapy combinations.